I'm sorry it took some time to get back to you! To my understanding, you started out with a guy bringing venereal disease to an isekaied world and it torpedoed from there, right? To the effects of that new disease, and what exactly the pre-isekai world was like, and how those cultures developed with those effects. Languages, research, crystals, religion, money... It's so large-scale! Which is comforting. I have a similar story (also inspired by isekai tropes! In my case, the rarity of black hair), but it's somewhat smaller-scale, and here I've realized that someone else out there had a similar idea. Seeing everyone else's reaction to your ideas, it reassures me a bit that though I'm writing my story for myself, someone out there will read my rambles sometime and actually like them just as much as I do. X)
Anyway!
We were talking about you and your story!
I looked at everything (skims, mostly) and found the only "common" simile that your story would use is probably the crystals. They are like our crystals, right? As far as I know, you haven't elaborated on what they're actually like (appearance), just what they're used for.
If they aren't hard, then nothing much else is popping into my head. XD Ahhh. I'm sorry.
P.S. Your youtube account is the one that joined on January 2, 2015, right?